The present invention relates to the manufacture of compositions from cellulose fiber material and the products obtained.
Many food and agricultural byproducts contain substantial amounts of cellulose. Cellulose is known to be useful in a wide range of markets. The food industry uses cellulose as a fat replacer, a component in products such as dietary fiber supplements, suspension agents, emulsifiers, water binding agents, as well as for edible films and coatings. The pharmaceutical industry uses cellulose as a component in bulking agents and dietary fibers for treatment and prevention of coronary heart disease, Type II diabetes, hypertension, diverticular disease, hemorrhoids, obesity, and so forth. Industrial applications of cellulose include use in filter medias, latex paint, and so forth.
Native cellulose fibers contain lignin, a polymeric material found in every type of vascular plant. Prior art processes for refining cellulose seek to remove lignin before any substantive treatment of the fibers. Lignin is known to cause cellulose fibers to stick together, thus reducing the surface area available for any subsequent reactions. It is believed that the presence of lignin also reduces the ability of cellulose microfibers to intertwine and entangle, thus reducing the structural integrity and/or strength of the final product.
Lignin removal is currently accomplished using extremely high temperatures and pressures. These extreme conditions cause raw material fragments to break apart, thus releasing the desired cellulose-based micro fibers. In addition, the raw materials are subjected to high concentrations of sodium hydroxide. See, for example, U.S. Pat. No. 5,817,381 to Chen, et al. Such a process is extremely energy-intensive in terms of the required temperatures and pressures. Further, the process produces a waste stream regarded as hazardous due to elevated pH levels caused by the use of large amounts of sodium hydroxide. Treatment of the waste stream adds to the cost of production and impacts the overall efficiency of this process.
Therefore, what is needed is a more efficient method of refining cellulose which is also safe for the environment.
The present invention comprises a method for refining cellulose comprising soaking raw material in NaOH having a concentration of about five (5) to 50% (dry basis) to produce soaked raw material which steeps for about 6 hours to allow the NaOH to work, refining the soaked raw material to produce refined material, dispersing the refined material to produce dispersed refined material, and homogenizing the dispersed refined material to produce highly refined cellulose (HRC) gel having a lignin concentration of at least about one (1)% and a water retention capacity (WRC) of about 25 to at least about 56 g H2O/g dry HRC. The method of the present invention produces a waste stream having a pH within a range of 8 to 9 and a reduced volume as compared to conventional cellulose refining processes.
In one embodiment, the method further comprises draining and washing the soaked raw material until the pH is down to about 8 to 9, bleaching the washed material at a temperature of about 20 to 100xc2x0 C. in hydrogen peroxide having a concentration of about one (1) to 20% dry basis, and washing and filtering the bleached material to produce a filtered material having a solids content of about thirty (30)%.
In one embodiment, the filtered material is refined by being passed through a plate refiner. The plate refiner essentially breaks up the lignin as it shreds the material into refined cellulose particles.
In another embodiment, a cellulosic material having a lignin concentration of about 10 to 20% is described having a WRC of about 25 to at least about 56 g H2O/g dry HRC. In another embodiment a HRC powder is described having a WRC of about 20 to 40 g H2O/g dry HRC. These functional characteristics are known to be related to average pore diameter and surface area of the HRC material.
The method of the present invention is energy efficient because it does not require high pressures and temperatures as in prior art processes. Despite the presence of higher lignin concentrations in the final product, the HRC gel of the present invention has a water holding capacity that is at least as good or better than prior art products. Use of a plate refiner to break up the lignin rather than using high concentrations of NaOH has the added advantage of producing a non-hazardous waste stream having pH within a range of 8 to 9 and a reduced volume.